On 2/26/07, Jeff Kashinsky <[EMAIL PROTECTED]> wrote: > I am building a 440 portable repeater out of a pair of GM300 radios and > a Harris Alpha mobile duplexer. > > I believe that I tuned the duplexer properly and it notches the xmit > signal by about 55db on the receive side. > > Using my signal generator as a source, it takes about 10db more signal > to key the contoller with the transmitter on than with it off. > > I am wondering if this is normal or if I have more work to do.
Depends on if you want it to work well or not. :-) I vote, more work. Are your measurements made when terminated into a good quality 50 ohm dummy load, or a real antenna system? Is there noise on your receive frequency (if hooked to an antenna)? Make sure you're using double-shielded good quality cables and connectors -- keep all that TX RF *in* the cables, and (hopefully) headed out the antenna. You don't want the TX cable leaking directly into the jumper from the receive side of the duplexer into the RX. (Kinda makes the duplexer worthless, ya know?) What power level is your TX set at? If you know you have 55dB of isolation, how much do you need to remove at the RX frequency? Is the TX clean? Do you have less desense if you turn the TX power down? What's the VSWR look like? Etc... Work from "known" things toward the unknown. You know (if you've tested it) at what level your receiver receives. You know how much power the TX is producing. You know if your antenna system is radiating all the power, or if some is getting reflected in the cabling. You next need to know what the TX does 5 MHz away, and whether or not 55dB of isolation is "enough". Nate WY0X
